BMI Biggest Contributor to Increase in Type 2 Diabetes in US

Pam Harrison

September 01, 2014

Rising obesity rates are the greatest contributor to the increasing prevalence of type 2 diabetes in the United States, accounting for all of the increase in women and about half of the increase in men, new comparative data from the National Health and Nutrition Examination Survey (NHANES) indicate.

The study is published in the September 2 issue of Annals of Internal Medicine.

"Body mass index [BMI] was the greatest contributor we saw to the increase in the prevalence [of type 2 diabetes] over time in both men and women," Andy Menke, PhD, senior research analyst, social and scientific systems, Silver Spring, Maryland, told Medscape Medical News.

"But unlike aging, race, and ethnicity, body mass can be changed. Studies have indicated obesity may be plateauing in the US — and that's a positive step — but we'd really like to see it start to decrease [because] our study suggests that we could see a much lower prevalence of diabetes if we were able to decrease overweight and obesity to the levels seen in 1976–1980," he noted.

The fact that BMI accounted for only about half of the increased prevalence of type 2 diabetes in men means the remainder of the rise is unexplained, Dr. Menke and colleagues stress.

Asked to comment, Robert O. Bonow, MD, American Heart Association spokesperson and professor of cardiology and director, Center for Cardiovascular Innovation, Northwestern University Feinberg School of Medicine, Chicago, Illinois, told Medscape Medical News that the study findings are exactly what would have been expected, as obesity and diabetes are clearly related.

"The biggest driver of diabetes is obesity across all ethnicities, maybe in particular in Hispanic Americans, but probably everybody," he said. Nevertheless, he feels it is important to have this relationship validated and show a strong relationship between obesity and diabetes because it underscores the need to curtail it.

Half of the Increased Risk in Men Unexplained

Investigators used data from NHANES II (1976–1980), NHANES III (1988–1994), and the continuous NHANES (1999–2002, 2003–2006, 2007–2010). The analysis involved 23,932 participants age 20 to 74 years.

Participants reported that they had been diagnosed with diabetes or had a fasting plasma glucose of at least 7.0 mmol/L (126 mg/dL) or higher.

The researchers note that NHANES does not determine whether a participant has type 1 or type 2 diabetes, but those with probable type 1 diabetes were excluded in a sensitivity analysis (those diagnosed before age 30 years who were receiving insulin within 1 year of diagnosis); the number of patients with type 1 diabetes was too small to have any meaningful effect on the results.

From 1976 to 1980 and 2007 to 2010, diabetes prevalence increased from 4.7% to 11.2% in men and 5.7% to 8.7% in women, respectively (P for trends for both groups < .001).After adjustment for age, race/ethnicity, and BMI, diabetes prevalence still showed an increase in men (6.2% to 9.6%; P for trend < .001), but not women (7.6% to 7.5%; P for trend = .69). Among the 3 covariates, BMI was the greatest contributor to change in prevalence estimates after adjustment, in both sexes.

In women, the prevalence of diabetes no longer increased over time after the researchers adjusted for BMI (P  =  0.80). In men, the increase in diabetes prevalence over time after adjustment for age, race/ethnicity, and BMI was approximately half the increase over time in unadjusted models.

"Changes over time in the distribution of age, race/ethnicity, and obesity in the population explained half of the increase in diabetes prevalence in men and the entire increase in diabetes prevalence in women," Dr. Menke emphasized.

"The substantial contribution of BMI to the prevalence of diabetes in both men and women supports ongoing public health efforts to address obesity, including developing effective interventions aimed at reducing obesity," he and his colleagues note.

However, they stress that they could not investigate other factors that may have increased the prevalence of diabetes among men. A drop in physical activity over time might be an important contributor, Dr. Menke suggested, but they could not explore this given the nature of the study.

So the fact that nearly half of the increase in diabetes in men remains unexplained "gives urgency to research investigating what additional factors may contribute to the faster rise in diabetes in men than in women," they conclude.

Findings Expected: Study Helps Link Obesity and Diabetes

Elaborating, Dr. Bonow said: "We know that with an aging population, we're getting more overweight and also more diabetes, and this study helps link them."

As to what society can do to stop the increasing prevalence of diabetes, he pointed to the many studies that show physical activity can both prevent diabetes in those at risk and improve diabetes symptoms in those who already have it.

He also emphasized the importance of diet: "not only portion control, but also the composition of the diet with an emphasis on more fruits and vegetables, and fewer carbohydrates."

The study was funded by the National Institute of Diabetes and Digestive and Kidney Diseases. Drs. Menke and Bonow have reported no relevant financial relationships.

Ann Intern Med. 2014;161(5):328-335. Abstract

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